1. Field of the Invention
In general, the invention relates to ovens and furnaces, and more particularly, to conveyor ovens.
2. Description of Related Art
Conveyor ovens are industrial ovens that are used in manufacturing processes. A typical conveyor oven includes an insulated, heated enclosure. Within the enclosure, a driven conveyor belt moves material from one end of the oven to the other. Conveyor ovens may be long, and they may have any number of “zones” that are maintained at different elevated temperatures. The temperature of the oven, the speed of the conveyor belt, the speed of air flowing within the conveyor oven, and the relative humidity of the air are usually regulated so that when the material emerges from the other end of the conveyor oven, a predefined heating process has been completed. Conveyor ovens are used to heat a wide variety of materials and products, ranging from foodstuffs to plastic films.
Because conveyor ovens are often very long, they are usually modular in construction—several modules may be connected together to form the complete oven. The joints between modules in a conveyor oven may, for example, be constructed with a tongue-and-groove approach, in which a protruding part of one module fits into a corresponding recess in the adjacent module to form a cohesive whole. Adjacent modules are often welded together, leaving some small distance between modules to allow for thermal expansion. The walls of a typical oven are constructed of layers of sheet metal with interspersed insulation.
Conveyor ovens often have a number of issues, some common to all heated enclosures and some specific. For one, thermal expansion, thermal stresses, fatigue, and fracture are all common issues. The issue of thermal expansion in a conveyor oven can be exacerbated by the fact that a typical oven includes components like idler rollers which rotate and support the belt, and which must remain free to rotate as the oven heats and expands.
Heat leakage is also a problem in conveyor ovens. Heat may escape through openings in the oven, and cold air from the surroundings may enter. Some of the heat loss may be through radiation, although these ovens typically have positive and/or negative pressure gradients that can push hot air out or pull cold air in. In many cases, a conveyor oven may have a positive pressure gradient at one point and a negative pressure gradient at another point, potentially exacerbating the problem. In fact, because of the size of a typical conveyor oven and the consequent number of potential leakage or trouble spots, even identifying the source of any leakage or loss can be a considerable undertaking. Moreover, within the oven itself, air and heat flows can also be an issue, and it can be difficult to maintain the desired temperature near the belt as the hot air circulates around the oven.
Aside from thermal issues, the mechanical strength of a typical oven can present some limitations. Because conveyor ovens are typically made of layers of sheet metal and insulation, there may or may not be sufficient mechanical strength to install secondary equipment within the oven.